Storybook yarn pnp support

[ndelangen]

Hey everyone 👋

Storybook has supported Yarn Plug'n'Play (PnP) since version 6; through custom resolvers, runtime APIs, CLI flags, and extra test coverage. Over time this has proven to be a maintenance burden. However, we've seen few active projects actually use PnP (less than 1%).

For these reasons, we:

1. Deprecated explicit PnP support in SB10 to give our PnP users fair warning. #32645
2. Plan to remove all PnP-specific code as part of SB11.

Many modern tools supports PnP natively, so it's possible that PnP projects will continue to work even after we've removed the code. At some point next year, we will release an SB11 alpha and share that below to give PnP users a chance to test things out.

Based on the response here, the test results in advance of SB11, and our usage telemetry, we'll make a final decision.

Thanks for your understanding!